Quinones with bromine

Second, metabolism of 6-fluoroBP by rat liver microsomes yields the same BP quinones obtained in the metabolism of BP (23). This suggests that these products are formed by an initial attack of a nucleophilic oxygen atom at C-6 in the 6-fluoroBP radical cation with displacement of the fluoro atom. In fact, when 6-fluoroBP is treated with the one-electron oxidant Mn(0Ac)3, the major products obtained are 6-acetoxyBP and a mixture of 1,6- and 3,6-diacetoxyBP (15), indicating that reaction occurs via an initial attack of acetate ion at C-6 of the 6-fluoroBP radical cation. On the other hand electrophilic substitution of 6-fluoroBP with bromine or deuterium ion shows no displacement of fluorine at C-6, although in both cases substitution occurs at C-l and/or C-3. These results indicate that... 

Introduction of oxygen into the molecule Oxidation with bromine, cerium(IV), H.O., HNO., NaNO.. Menadiol to the quinone [239], lidocaine to its N-oxide [207], chloropromazine to its sulphoxide [212]. 

Tribromo-m-cresol is oxidized by chromium trioxide in 70% acetic acid at 70-75 °C within 10 min to dibromo-m-toluquinone (3,5-dibromo-2-methyl-p-benzophenone) in 77% yield [559]. 2-BVomo-4-hy-droxy-5-methoxybenzyl alcohol treated with Fremy salt at pH 6 at room temperature for 1 h gives an 84% yield of 2-bromo-5-methoxy -benzo-quinone [487]. 4-Benzyl-2,6-dibromophenol, on oxidation with bromine in a sealed tube, yields 2,6-dibromophenylchinomethide [732] (equation 312). The oxidation of 2,5-di-tert-butyl-4-methoxyphenol with mercuric oxide or... 

Use of quinones like chloranil and DDQ has also been employed for this dehydrogenation. Halogenation-elimination with bromine or NBS has been a chemical means to promote the dehydrogenation. However, with the bromination/elimination protocol, one must be careful as aromatic halogenation can occur. 

Within the cubane synthesis the initially produced cyclobutadiene moiety (see p. 329) is only stable as an iron(O) complex (M. Avram, 1964 G.F. Emerson, 1965 M.P. Cava, 1967). When this complex is destroyed by oxidation with cerium(lV) in the presence of a dienophilic quinone derivative, the cycloaddition takes place immediately. Irradiation leads to a further cyclobutane ring closure. The cubane synthesis also exemplifies another general approach to cyclobutane derivatives. This starts with cyclopentanone or cyclohexane-dione derivatives which are brominated and treated with strong base. A Favorskii rearrangement then leads to ring contraction (J.C. Barborak, 1966). 

The procedure described is essentially that of Belleau and Weinberg and represents the only known way of obtaining the title compound. One other quinone acetal, 1,4,9,12-t6traoxadispiro[4.2.4.2]tetradeea-6,13-diene, has been synthesized by a conventional method (reaction of 1,4-cyclohexanedione with ethylene glycol followed by bromination and dehydrobromination ) as well as by an electrochemical method (anodic oxidation of 2,2-(l,4-phenylenedioxy)diethanol ). Quinone acetals have been used as intermediates in the synthesis of 4,4-dimethoxy-2,5-cyclohexadienone,. syw-bishomoquinone, - and compounds related to natural products. ... 

Porco s route to (—)-kinamycin C (3) began with 2,5-dihydroxybenzaldehyde (38), which was elaborated to the enone 35 by the sequence shown in Scheme 3.6. Regioselective bromination [25] followed by methylation and reduction of the aldehyde function afforded the primary alcohol 39. The alcohol 39 was dearomatized by treatment with bis(acetoxy)iodobenzene, to afford the quinone monoketal 41. Transketalization with 1,3-propanediol followed by silylation of the primary alcohol generated the silyl ether 42 in 72 % yield over three steps. 

The oxidative metabolism leads to the formation of reactive species (epoxides, quinone-imines, etc.), which can be a source of toxicity. Consequently, slowing down or limiting these oxidations is an important second target in medicinal chemistry. Thus, the metabolism of halothan (the first modern general anaesthetic) provides hepatotoxic metabolites inducing an important rate of hepatitis the oxidation of the non-fluorinated carbon generates trifluoroacetyl chloride. The latter can react with proteins and lead to immunotoxic adducts [54], The replacement of bromine or chlorine atoms by additional fluorine atoms has led to new families of compounds, preferentially excreted by pulmonary way. These molecules undergo only a very weak metabolism rate (1-3%) [54,55]. 

Brominated condensation products can be obtained by using appropriately halogenated naphthoxidine intermediates such as 19. For example, 19 can be condensed with aniline in acetic acid at 90 °C to give 20 [1], Naphthoxidine and its brominated derivatives can also be condensed with aminoazo compounds to give mixed azo-quinone chromogens, e.g., 21. These are of interest as homogeneous green dyes [1]. 

Benzofuroxans are formed from o-quinone dioximes by oxidation with, for example, alkaline ferricyanide, nitric acid, bromine water and chlorine, While the reaction is usually straightforward and high yielding the method is not generally applicable since the dioximes themselves are not readily obtainable and are often best prepared via reduction of the furoxan (see Section 4.22.3.1.3). However it can be used when the parent quinones or their monooximes (o-nitrosophenols) are available from other sources. Thus it is the method of choice for the acenaphtho- and phenanthro-furoxans, (18) and (94 n = 1), respectively. In other cases alternative routes, such as the oxidation of o-nitroanilines or the thermolysis of o-nitroaryl azides, are more commonly utilized. 

Reaction of pentafluorophenol with rerf-butyl hypobromite starts as an electrophilic substitution in the benzene ring. The electrophile is formed by dissociation of tert-butyl hypobromite to tert-butoxy anion and bromine cation. The bromine cation attacks the para position and forms a positively charged Wheland complex, a nonaromatic species that is converted by ejection of proton from the phenolic hydroxyl to a quinon-oid compound, 4-bromopentafluorocyclohexa-2,5-dienone [39]. 

Phenol reacts with three equivalents of bromine in CC14 (in the dark) to give a product of formula Cg OB. When this product is added to bromine water, a yellow solid of molecular formula C6H2OBr4 precipitates out of the solution. The IR spectrum of the yellow precipitate shows a strong absorption (much like that of a quinone) around 1680 cm-1. Propose structures for the two products. 

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